1. Field of the Invention
The present invention relates to an LED backlight device in which a many light emitting diodes (LEDs) serve as light sources.
2. Description of the Related Art
An LED backlight device is, for example, assembled to a display panel (such as a liquid display panel), and illumination light emitted from each LED is supplied to a display panel unit, to form a display device. Compared to, for example, a cold cathode fluorescent lamp (CCFL), which is generally used as a light source in a related art, the LED backlight device is provided with many LEDs which are low in cost and which have various characteristics, such as being small in size/being light, having low electrical power consumption, or high luminance, so that image display of high luminance is performed even for a large display device.
In the LED backlight device, improvement in each LED has caused an increase in the luminance and a reduction in an individual heat value. However, by providing the LED backlight device with more LEDs due to an increase in the size of the display device, its overall heat value is also large. In addition, in the LED backlight device, since a light-guiding space, which is externally shielded from light, is formed at a back-surface side of the display panel unit for assembly of the LED backlight device, heat generated from each LED is confined in the light-guiding space in a sealed state. Therefore, the overall temperature is high.
In the LED backlight device, the chromaticity of each LED may become an improper value or the life of each LED may be reduced due to light-emission characteristics of each LED becoming unstable under a high-temperature environment. In the LED backlight device, in particular, a reduction in light-emission efficiency of a red LED under a high-temperature environment is reduced, thereby reducing color reproducibility. The effect of higher temperature in the display device not only gives rise to the aforementioned problems in the LED backlight device, but also gives rise to problems such as reducing the life and deteriorating the characteristics of, for example, an integrated circuit device or electronic components mounted to various circuit unit substrates.
With regard to the problem of the LED backlight device, the applicant has provided heat-dissipating devices. Each of these heat-dissipating devices restricts a rise in temperature of the entire backlight device by efficiently dissipating heat generated from, for example, a circuit block or heat generated from each LED. The heat is efficiently dissipated using a heat pipe having a very high heat conveyance efficiency. (Refer to, for example, Japanese Unexamined Patent Application Publication Nos. 2005-317480 and 2006-58487.)
Each of these heat-dissipating devices of the previous applications is formed by connecting a heat-conveying unit to a heat-dissipating unit. The heat-conveying unit for generating heat is formed by mounting an aluminum heat-dissipating plate to the back surface of a wiring board (on which many LEDs are disposed in lines and are mounted) and by mounting a heat pipe to the heat-dissipating plate. The heat-dissipating unit includes a heat sink and a cooling fan and is disposed at a side of a bottom chassis. In each of the heat-dissipating devices of the previous applications, the heat generated from, for example, each LED is efficiently conveyed to a side by the heat pipe through the heat-dissipating plate, and the heat sink and the cooling fan efficiently dissipate the heat to the outside for efficient cooling. This reduces the overall temperature rise, so that each LED is stably driven.